unphysical solution near boundary

Tobias · May 8, 2009, 06:42

Hello!

My name is Tobias and I have a strange problem. I made a model of a duct with simple obstacles. fluid is iawps steam table. Boundary condition is static pressure@ outlet, mass flow rate with direction an total temperature @ inlet. the inlet is quite long with free slip walls and no significant change in the flow is estimated. Now, if I change the inlet temperature (increase 200K), the first node inside the model is not affected and there is a unphysical drop of temperature within the first cell. the residuals become very low anyway. the mesh is quite coarse at the inlet but i think that the boundary should not be affected. aspect ratio is ok and angle, too.

I do not know why the solver "ignores" my new inlet temperature.

Thank you very much for any idea.

Tobias · May 8, 2009, 11:06

The problem seems to be the steam table. If I choose another one built by myself with taskflow, everything is fine.

ghorrocks · May 10, 2009, 23:34

Hi,

The IAPWS database makes convergence a bit trickier. Are you sure your table values are OK? Check you have not gone over the limits (min/max temperature, pressure etc) you have defined for you properties table. You might also need to put a few extra points in.

Glenn Horrocks

May 8, 2009, 06:42	unphysical solution near boundary	#1
Tobias New Member Tobias Krawuttke Join Date: May 2009 Posts: 15 Rep Power: 16	Hello! My name is Tobias and I have a strange problem. I made a model of a duct with simple obstacles. fluid is iawps steam table. Boundary condition is static pressure@ outlet, mass flow rate with direction an total temperature @ inlet. the inlet is quite long with free slip walls and no significant change in the flow is estimated. Now, if I change the inlet temperature (increase 200K), the first node inside the model is not affected and there is a unphysical drop of temperature within the first cell. the residuals become very low anyway. the mesh is quite coarse at the inlet but i think that the boundary should not be affected. aspect ratio is ok and angle, too. I do not know why the solver "ignores" my new inlet temperature. Thank you very much for any idea.

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May 8, 2009, 11:06		#2
Tobias New Member Tobias Krawuttke Join Date: May 2009 Posts: 15 Rep Power: 16	The problem seems to be the steam table. If I choose another one built by myself with taskflow, everything is fine.

May 10, 2009, 23:34		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	Hi, The IAPWS database makes convergence a bit trickier. Are you sure your table values are OK? Check you have not gone over the limits (min/max temperature, pressure etc) you have defined for you properties table. You might also need to put a few extra points in. Glenn Horrocks